This invention relates to ultrasonic transducers and, more particularly, to an ultrasonic transducer with a magnetostrictive lens for dynamically focussing and steering a beam of ultrasound energy.
Ultrasonic transducers for medical or industrial applications are constructed from one or more piezoelectric elements sandwiched between a pair of electrodes. Such piezoelectric elements are typically constructed of lead zirconate titanate (PZT), polyvinylidene difluoride (PVDF), or PZT ceramic/polymer composite. The electrodes are connected to a voltage source, and when a voltage is applied, the piezoelectric elements are excited at a frequency corresponding to that of the applied voltage. When a voltage pulse is applied, the piezoelectric element emits an ultrasonic beam into the media to which it is coupled at the frequencies contained in the excitation pulse. Conversely, when an ultrasonic beam strikes the piezoelectric element, the element produces a corresponding voltage across its electrodes. Typically, the front of the element is covered with an acoustic beam matching layer that improves the coupling with the media in which the ultrasonic beams propagate. In addition, a backing material is disposed to the rear of the piezoelectric element to absorb ultrasonic beams that emerge from the back side of the element so that they do not interfere. A number of such ultrasonic transducer constructions are disclosed in U.S. Pat. Nos. 4,217,684, 4,425,525, 4,441,503, and 4,470,305, all of which are assigned to the instant assignee.
When used for ultrasound imaging, the transducer typically has a number of piezoelectric elements arranged in an array and driven with separate voltages (apodizing). By controlling the time delay (or phase) and amplitude of the applied voltages, the ultrasonic beams produced by the piezoelectric elements combine to produce a net ultrasonic beam focused at a selected point. By controlling the time delay and amplitude of the applied voltages, this focal point can be selectively moved in a plane to scan the region of interest to be imaged.
This form of ultrasonic imaging is referred to as "phased array sector scanning", or "PASS". The PASS technique is comprised of a series of measurements in which the steered ultrasonic beam is transmitted into the region of interest. A system using the PASS technique then switches to a receive mode after a short time interval, and the reflected ultrasonic beam is received and stored. Typically, the transmission and reception are steered in the same direction during each measurement to methodically acquire data from a series of focal points along a scan line. The time required to conduct the entire scan is a function of the time required to make each measurement and the number of measurements required to cover the entire region of interest at the desired resolution and signal-to-noise ratio. For example, a total of 128 scans lines may be acquired over a 90 degree sector, with each scan line being steered in increments of 0.70.degree.. A number of such ultrasonic imaging systems are disclosed in U.S. Pat. Nos. 4,155,258, 4,155,260, 4,154,113, 4,155,259, 4,180,790, 4,470,303, 4,662,223, 4,669,314 and 4,809,184, all of which are assigned to the instant assignee.
Although PASS techniques provide significant inspection capability, implementing such dynamic focussing usually requires a large number of electronic components to impart the time delays (and/or phase shifts) to the signals from each transducer array element. The use of such large number of electronic components significantly adds to the cost and complexity of the imaging system. In an effort to reduce the number of electronics components such PASS techniques may sometimes require moving the transducer relative to the region of interest. In this case use of a manipulator, to provide such relative movement between the transducer and the region of interest, may be required which similarly adds to the complexity and cost of the system. Thus, there is need in the art to provide an improved ultrasonic transducer which is capable of dynamically focussing and steering a beam of ultrasonic energy in a manner which does not require use of either a large number of electronic components or of a manipulator and thus effectively reduces the cost and complexity required to achieve dynamic focussing and steering of beams of ultrasound energy. Moreover, the transducer of the present invention can be conveniently used as an adjunct in present systems using such PASS techniques to provide three-dimensional scanning of the region of interest to be imaged.